This invention relates to two-cycle internal combustion engines and, more particularly, to two-cycle internal combustion engines including air scavenging.
The cylinder of two-cycle internal combustion engines typically includes a combustion chamber having one or more exhaust ports and one or more fuel intake ports which are covered by the piston during the piston compression or upstroke and are uncovered during the piston expansion or downstroke. The exhaust port(s) is opened first during the piston downstroke to permit the combustion gases to be exhausted from the combustion chamber. The fuel intake ports are subsequently opened to admit an air-fuel mixture, which is compressed in the engine crankcase during the piston downstroke, into the combustion chamber. The incoming pressurized air-fuel mixture flows toward the exhaust port(s) and scavenges or expels remaining combustion gases from the combustion chamber.
In cross-scavenged engines, the exhaust and fuel intake ports generally are diametrically opposed and the top end of the piston includes a baffle arranged to direct the flow of the incoming air-fuel mixture upwardly. A loop-scavenged engine includes side fuel intake ports which are arranged to introduce a portion of the air-fuel mixture into the combustion chamber at an angle so as to promote a swirling action. In either type, a considerable amount of the uncombusted air-fuel mixture can be lost through the exhaust port(s) during the scavenging of the combustion gases from the combustion chamber, resulting in ineffiency and an increase in polluting emissions.
One proposed approach for minimizing overscavenging involves scavenging the combustion chamber with air only during most of or the entire downstroke of the piston and thereafter injecting fuel into the combustion chamber. This approach requires a fuel injection system and costly controls. Also, the power produced by the engine at high speeds and loads is less than that produced by conventional engines because there is insufficient time for the fuel and air to mix prior to combustion.
Another proposed approach involves introducing an air-fuel mixture from a carburetor directly into the combustion chamber through a fuel intake port located farthest away from the exhaust port and drawing air into the engine crankcase and then introducing air from the crankcase into the combustion chamber through one or more intake ports located closer to the exhaust port. A further proposed approach involves the use of a chamber which is exterior to and separated from the crankcase by a flexible membrane for pumping air into one or more intake ports.
Attention is directed to the following U.S. patents:
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Bezu 1,527,166 February 24, 1925 De Waern 2,406,491 August 27, 1946 Von Seggern et al. 3,363,611 January 16, 1968 Iwai 4,075,985 February 28, 1978 ______________________________________
Attention is also directed to British Patent No. 703,916.